The invention relates to synchronizing hydraulic actuators and has a particular application in simultaneously actuating the moving flaps of variable exhaust section nozzles of turbojets. Nevertheless, the invention can be used in other applications, for example for actuating a control ring for controlling variable-angle blades in a stator for a gas turbine compressor.
In a known embodiment of a variable section nozzle, the moving flaps are actuated by means of a set of hydraulic actuators acting on controlled flaps which in turn entrain follower flaps. The controlled flaps are actuated by links hinged to the rods of the actuators or to a common control ring on which the actuators act. Mechanical means ensure that the controlled flaps are synchronized independently of the follower flaps which are not synchronized. Such a nozzle, whose mechanical design ensures that it is self-synchronizing, presents drawbacks in terms of cost and mass and because of the presence of parts that are caused to rub against one another while hot.
Another solution consists in controlling the set of flaps synchronously in order to avoid friction or even jamming between flaps, which requires increased actuator force and can lead to damage that affects the lifetime of the flaps, with the synchronization function being taken over by the actuators.
Unfortunately, because of inevitable dispersion in characteristics, it is known that it is not possible in practice to achieve simultaneous displacement of actuator rods, even when the actuators are controlled from a common hydraulic fluid manifold.
In order to solve that problem, proposals are made in document FR 96/14565 to implement a mechanical connection between the pistons of the actuators by means of a toothed ring which meshes with gearwheels, each coupled to an actuator piston by a screw-and-nut system which transforms the translation movement of the piston into rotary movement of the gearwheel.
Such a synchronizing device does indeed make it possible to ensure that the pistons of the actuators are displaced simultaneously, but it requires a toothed ring that is capable of transmitting the forces needed to overcome the differences in displacement between pistons, and thus a ring that is relatively massive and bulky.